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Basic Measuring
Instruments
*There are 3 types of instruments we use in 50A:
*Ammeter
*Voltmeter
*Ohmmeter
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*To understand loading effects
*To understand a practical use for series and
parallel circuits
*To what you are doing when you use them
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Ammeter
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Ammeter
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Ammeter
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Ammeter
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Ammeter
* When you turn the knob to
change scales on an ammeter,
you are changing the shunt
resistor.
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* AN IDEAL AMMETER HAS 0 OHMS OF
INTERNAL RESISTANCE!!
* Since no ammeter is perfect, the
result is called loading effects.
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http://www.youtube.
com/watch?v=lkwh4Z
axHIA&feature=email
What about Voltmeters?
Voltmeter
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Voltmeter
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Voltmeter
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Multi-range Voltmeter
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* AN IDEAL VOLTMETER HAS ∞ OHMS OF
INTERNAL RESISTANCE!!
* Since no voltmeter is perfect, the
result is called loading effects.
Multi-range Voltmeter
Voltmeter sensitivity is expressed in ohms/volt (Ω/V). A voltmeter is
considered more sensitive if it draws less current from the circuit.
The sensitivity of a voltmeter that draws 50uA is the inverse of this,
20,000 ohm per volt.
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voltmeter sensitivity
Multi-range Voltmeter
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Multi-range Voltmeter
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* The internal resistance of our DMM is
always 10MΩ no matter range is selected.
(That’s because there is no range to select.
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51.3V
95.2kΩ
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Loading Effects
48.7V
What about Ohmmeters?
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What about Ohmmeters?
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What about Ohmmeters?
Ammeter
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